Conventionally, a metal wiring board obtained by forming a wiring including a metal pattern on a surface of an insulating substrate has been widely used in electronic parts or semiconductor elements.
As a method of producing such a metal pattern material, a “subtractive method” is mainly used. The subtractive method includes: disposing, on a metal film formed on a surface of a substrate, a photosensitive layer which is sensitized by irradiating with an actinic ray; imagewise exposing the photosensitive layer, then developing the photosensitive layer to form a resist image; subsequently etching the metal film to form a metal pattern; and finally pealing off the resist.
In the metal pattern obtained by the above method, adhesion between the substrate and the metal film is realized due to an anchoring effect generated by providing irregularities on the surface of the substrate. Therefore, owing to the irregularities at a substrate interface portion of the obtained metal pattern, there has been a problem in that high frequency characteristics are deteriorated when the metal pattern is used as a metal wiring. Further, since the surface of the substrate needs to be treated with a strong acid, such as chromic acid or the like, for roughening the surface of the substrate, there has been a problem in that a complicated process is required in order to obtain a metal pattern that exhibits excellent adhesion between a metal film and a substrate.
In order to solve the above problems, a method has been proposed, which includes forming, on a substrate, a cured layer containing a polymer having a chelating ligand capable of trapping a metal ion that serves as a plating catalyst, and performing plating with respect to the cured layer (see, for example, Patent Document 1). In this method, a composition prepared by simultaneously mixing the polymer and a curing agent is used for the formation of the cured layer containing the polymer having a chelating ligand. However, the composition has a concern about stability over time thereof, and may cause a problem in that a uniform cured film cannot be obtained.
Further, in the method described in Patent Document 1, the ligands exemplified as examples of the chelating ligand include carboxylic acid type ligands represented by iminodiacetic acid, azo type ligands, polyamine type ligands, polyimine type ligands, alcoholic or phenolic hydroxyl type ligands, and β-diketone type ligands, all of which are hydrophilic. Therefore, according to this method, moisture is readily absorbed or desorbed due to variation in temperature or humidity, resulting in a problem in that the formed metal film or the substrate is distorted in shape or the metal film is readily peeled off from the substrate.
Further, using a roughening technique (for example, desmear etching) for realizing adhesion or for removing residual resins from via holes (hereinafter, may also be referred to as “via”) is generally known (see, for example, Patent Document 2). However, in the case of using a metal etching method such as a subtractive method or a semi-additive method for forming a fine wiring, the roughening includes great demerits such that the adhesive force to the micronized wiring is decreased and the formation of a fine metal wiring itself is difficult since it becomes hard to remove metal residues which are incorporated in the roughened face between the wiring lines and thus, over-etching may readily occur at the time of etching.
Therefore, it is preferable that the roughened surface is smoothed, before realizing strong adhesion to a metal. However, for example, the substrate is roughened by a desmear treatment performed at the time of via formation. In production of a multilayer substrate, substrate roughening is important also in view of securing satisfactory adhesion in laminated layers including, for example, an interlayer insulating film or a solder resist. Thus, under the existing circumstances, production of a fine wiring board, only by means of merely forming a strong adhesive metal wiring on a smooth substrate surface, is difficult.    [Patent Document 1] Japanese Patent Application Laid-Open (JP-A) No. 11-12504    [Patent Document 2] JP-A No. 2001-85840